The semi-trailers available for automotive vehicle transportation used for under-developed highways, present complex monobloc constructions, requiring about twenty different types of metallic profiles. Such structures comprise: a fixed lower structural platform provided with parallel longitudinal rails on which the vehicle being transported rolls, which are vertically displaceable in at least two portions in order to provide access to two levels of the trailer. Such semi-trailers have side structures of rigid lattice work between columns. There also is an upper platform, comprising two longitudinal rails supported by crossbars with the upper platform's front being pivotable or not on the structure in order to permit a selective vertical angular displacement of its rear portion for loading and unloading operations maintaining, however, its cruising height constant.
Access to the above-described semi-trailer is effected by its rear end, by means of rails fittable to the lower platform rails which are rearwardly slidable and rest on the ground to provide an access ramp.
Apart from requiring a great number of manual operations for loading and unloading, thereby demanding considerable operation time and physical effort from the operator, the existing constructions have serious technical limitations which altogether considerably limit their mobility and versatility, such as:
the trailer structures are usually over-dimensioned, excessively rigid and, due to the trailer usually using low-course suspensions, vibrations due to highway unevenness are transmitted to the structure, subjecting it to frequent fractures due to material fatigue;
the lower platform permits only limited motion making it difficult to overcome the trailer's wheel box and turntable, resulting in very steep access slopes, especially hindering the maneuverability of low ground-clearance vehicles. Such a construction requires the lowering of the lower platform between the wheel boxes and the front columns of the semi-trailer, forming a so-called "bore", thereby increasing difficulty in accessibility and usually limiting the trailer to transporting only small vehicles;
the upper platform is normally fixed, limiting due to maximum legally permitted cruise heights, the models of vehicles it can carry, generally up to five automobiles, except for light commercial vehicles since these have excessive height. This further limits the space available between platforms, apart from providing excessively steep inclination to the loading/unloading ramp;
the lattice work hinders the full opening of the doors of the vehicles loaded on the lower platform, hence frequently causing damage to the driver's door during its opening for maneuvering of the loaded vehicle;
due to difficulties in accommodating its cargos, the existing semi-trailers have essentially non-homogeneous weight distribution, thereby subjecting their structure and wheel train shaft to additional stressess, increasing maintenance problems thus reducing considerably the durability of the semi-trailer.
Due to the existence of the "bore", to permit access of a vehicle to the berth provided over the tractor's turntable, as well as to optimize its load capacity, which usually is a maximum of eleven automobiles, including in some embodiments a vehicle transported on a structure provided over the tractor, the semitrailer is usually provided with two remount platforms. These platforms are mounted cross-wise on the side columns of said semitrailer, with the remount platforms being vertically displaceable between a lower loading position and an upper non-operative position. Each remount platform carries a vehicle partially superposed or "inserted" between an automobile in the "bore" and the upper platform. This type of embodiment presents a shortcoming due to problems in the remount platform locking means. Due to vibrations from the highway, and consequent shaking of the remount platforms, damages occur due to impacts between remounted vehicles and those traveling in the "bore".
Over the course of time, industry in countries such as Brazil has adopted numerous alterations for semi-trailers for automotive vehicle transportation, envisaging solving the main above-mentioned problems, as well as other less important ones.
Solutions were experimented with, such as using two two-wheel trains, instead of the traditional single four-wheel train in order to obtain a larger track. This permitted lowering the semi-trailer's lower platform, hence eliminating the "bore". While this structure provides highly increased mobility and versatility to the semi-trailer, it gives rise to stability problems and risk of accident in situations such as, for example, when a tire fails.
Most of the solutions adopted to date envisage other structurally and operationally optimizing vehicle-carrying semi-trailers. These also have turned out to be ineffective occasionally solving specific problems but having other limitations.
Semi-trailers use in countries with developed road systems have highly articulated constructions, individually operable upper platforms, soft suspensions and minimal ground clearances (of up to 10 cm.), and in general are fully hydraulically and/or pneumatically actuated. Such constructions are also inadequate for third world conditions, due to their high costs (up to five times higher than locally built semi-trailers).